It is important for future space mission requirements, such as with space platforms, that a clean environment be maintained near the space platform or vehicle. Reaction control system thrusters, turbines or the like can be major contributors to contaminants in the immediate environment. Bi-propellant thrusters can be particularly objectionable because they exhaust products of combustion into the surrounding environment.
In particular, some of the problems created are that contaminants comprise noise sources for passive and active sensors. Particulates and condensibles can become deposited on surfaces, thereby degrading, impairing and in some instances destroying components vital to the space mission. Some vapors actually will attack and degrade various materials. Laser-optical mirrors are particularly sensitive to contaminants. Soot from hydrocarbon-based fuels, such as monomethyl hydrazine, can become deposited on the mirrors, and water vapor can degrade the mirror coatings. Changes in mirror absorptivity due to these contaminants can cause hot spots on the mirror and, at the very least, cause a degraded performance from thermal distortion or, in the worst instances, completely destroying the mirror.
The use of cold gas jets are desirable from a contamination viewpoint since the propellant is a non-condensible, non-reactive gas. However, cold gas jets have a low specific impulse which imposes a weight penalty. Although bi-propellant and hydrazine thrusters have specific impulses, their reaction products (Soot, CO, CO.sub.2, H.sub.2 O, NH3, etc.) are objectionable. Even H.sub.2 O.sub.2 thrusters developed for space mission use will spew water vapor into the environment.
There is a need for integrating the high specific impulse of a bi-propellant thruster with the environmental acceptability of a cold gas thruster. The present invention is directed to satisfying this need and solving the problems itemized above.